Diffusion transfer photography is well known and has been utilized to provide "instant" images in black and white in both a peel-apart format and an integral format. For example, U.S. Pat. No. 2,543,181 describes instant peel-apart black and white silver transfer films and U.S. Pat. No. 4,489,152 describes instant integral black and white silver transfer films.
Diffusion transfer photographic film units which include photosensitive silver halide for forming images typically comprise a support carrying a photosensitive silver halide emulsion, a silver halide solvent, a silver reducing agent for converting the exposed silver halide to metallic silver and an alkaline activator to obtain a pH at which the silver halide can be effectively developed. A visible image is formed in these materials by exposing the photosensitive silver halide to an imagewise pattern of activating light to form a latent image, dissolving the unexposed silver halide, transferring the dissolved unexposed silver halide to an image-receiving layer and reducing the transferred unexposed silver halide to form a positive image in reduced silver.
It is well known in the art that light used to expose the photosensitive silver halide emulsion of a diffusion transfer photographic film unit may be diffusely transmitted therethrough to the support and, then be reflected back to the emulsion causing it to be reexposed. Given the distance of the support and the interfaces (of the other layers of the film unit between the support and the emulsion layer) from the emulsion layer, the reexposure of the emulsion occurs at points laterally removed from the initial exposure, hence, with reexposure by such reflected light, a "halo" appears around the site of initial exposure of the emulsion. As will be appreciated by one of skill in the relevant art, the halo effect or "halation" reduces the resolution or sharpness of the film and, accordingly, of the resultant image produced by such film.
As would be understood by those of skill in the art, halation may be substantially prevented or reduced by absorbing any light which may be transmitted by the photosensitive silver halide emulsion layer. It is generally known in the art to prevent halation by, for example, coating the support of the film unit remote from where the exposure is made with either dyes or pigments, or coating an antihalation layer which contains gelatin and dyes or silver between the support of the film unit remote from where the exposure is made and the photosensitive silver halide emulsion layer. Generally, the antihalation dyes incorporated within an antihalation layer are either bleached, decolorized or removed from the layer after photographic processing, e.g., to prevent its color from reappearing in time as it is slowly reoxidized, while antihalation dyes or pigments incorporated in the support remain.
U.S. Pat. No. 4,039,333 is directed to an antihalation layer and describes photographic materials for use in conventional photography which include a combination of at least two particular binders together with an antihalation material, e.g., carbon black, which provide improved antihalation.
U.S. Pat. No. 4,751,174 is directed to a silver halide photographic material for use in conventional photography and describes the inclusion of a light-insensitive silver halide emulsion layer between a light-sensitive silver halide emulsion layer and the support which decreases halation.
U.S. Pat. No. 4,957,856 is directed to a subbing layer having a decoloring capable antihalation function and describes a silver halide photographic material for use in conventional photography which includes the subbing layer which comprises a binder, a polymer, i.e., mordant, described therein, a dye described therein and a surface active agent. As reported therein, the particular mordant and dye combination improves the processing time decolorization.
U.S. Pat. No. 4,990,432 is directed to a silver halide photographic light-sensitive material for use in conventional photography and which includes a reflective support having a transmission density of not more than 0.8, a silver halide emulsion layer and an antihalation layer formed closer to the support than the silver halide emulsion layer. As reported therein, the antihalation layer prevents any reflected light incident into the silver halide emulsion layer.
U.S. Pat. No. 5,318,885 is directed to an antihalation layer and describes a photographic element for use in conventional photography which includes a reflective support, one or more photosensitive silver halide emulsion layers, and a colored, i.e., blue or gray grains of silver in the form of platelets, antihalation layer interposed between the support and the photosensitive layers.
U.S. Pat. No. 5,665,528 is directed to a quickly decolorized new antihalation dye which is incorporated in an antihalation layer of a silver halide photographic material that is conventionally processed.
Diffusion transfer color photographic integral-type film units are known in the art, such as described, for example, in U.S. Pat. No. 5,422,233, which include layers comprising image-forming materials, e.g., dye developers, interposed between an opaque support and a photosensitive silver halide emulsion layer, which may also function as antihalation layers given the light absorption ability of the dye developers. Black and white diffusion transfer photographic film units, by definition, do not contain such color image-forming materials and, therefore, generally contain some provision for antihalation.
The integral black and white instant films described in U.S. Pat. No. 4,489,152 include an opaque layer, i.e., carbon black and polyvinylpyrrolidone, between the silver halide emulsion layer and the image-receiving layer so that the film unit may be developed outside the camera, and a light-reflecting layer, i.e., a white layer of titanium dioxide, positioned between the carbon black layer and the image-receiving layer to provide a white background against which the silver transfer image may be viewed. It would be understood by those of skill in the relevant art that the carbon black layer disclosed therein would be able to function as an antihalation layer, i.e., absorb substantially all of, if not all of, the light which passed through the emulsion layer during photoexposure.
U.S. Pat. No. 4,078,933 is directed to a silver halide photographic light-sensitive element for use in conventional photography which includes at least one silver halide emulsion layer and at least one hydrophilic colloid layer containing at least one dye wherein the dye is useful in antihalation and can be decolorized readily and completely. According to the description provided therein, to be satisfactory, the subject dyes must be photographically inert, have a good mordanting property, i.e., remain in the layer, and be decolorized or removed by dissolving during photographic processing, i.e., good bleachability.
U.S. Pat. No. 4,294,917 is directed to a dye antihalation layer and describes a photographic silver halide material for use in conventional photography which includes in at least one layer a solid dispersion of a water-insoluble antihalation dye. As reported therein, after completion of the conventional photographic processing, no dye in the antihalation underlayer was visible and, the dye was completely and irreversibly destroyed in the silver halide developing solution and no discolouration of any of the processing solutions was visible.
It is known in the art that use of antihalation materials may result in a loss of emulsion sensitivity or speed. Methods have been devised to reduce such losses in speed associated with the use of antihalation materials, by, for example, incorporating a layer of a light-reflecting pigment, such as, for example, titanium dioxide, e.g., in between the support containing the antihalation materials and the photosensitive silver halide emulsion layer of the film unit, or, in between the antihalation layer and the photosensitive silver halide emulsion layer, preferably, adjacent the photosensitive silver halide emulsion layer. The reflecting layer reflects back substantially all of the exposure light to the silver halide emulsion and, given the proximity of the reflecting layer to the photosensitive silver halide emulsion layer, causes reexposure to made in substantially the same point as the original exposure, hence, preventing "halo" formation, such as described, for example, in U.S. Pat. No. 4,563,406 which describes a photographic support coated with, in succession, a colorant layer (antihalation layer), a white pigment layer and a silver halide emulsion layer; or, U.S. Pat. No. 4,615,966 which describes a diffusion transfer photographic instant film unit which includes a light-reflecting spacer layer disposed between a silver halide layer and the associated layer of image dye-providing material to increase effective film speed as a result of the reflection of light back to the silver halide.
While such methods of preventing or reducing halation in photographic elements have been found to provide advantageous results as are described in the above-mentioned patents, nevertheless their performance in some photographic systems is not completely satisfactory. For example, in some diffusion transfer photographic systems, the use of such methods have been found to contribute to undesirable silver image resolution and speed loss thereby adversely affecting the aesthetic qualities of the final photograph.
It would be desirable to have diffusion transfer photographic black and white film units which include suitable antihalation materials, and which, at the same time, provide suitable film speed and resolution in the finished photograph, and suitable sharpness as visually perceived.
As the state of the art for diffusion transfer photographic film units continues to move forward, new techniques and materials continue to be developed by those of skill in the art in order to meet the performance criteria required of such materials. The present invention is drawn to novel diffusion transfer black and white photosensitive film units which include an antihalation layer comprising an antihalation material, titanium dioxide and a binder; an aqueous alkaline processing composition which includes a suitable amount of a light-reflecting pigment, preferably, titanium dioxide, to form a light-reflecting layer during photographic processing which provides a white background against which to view the final image; a silver reducing agent; and a silver halide solvent.